This invention relates to electromechanical clothing dryer timers where a component of the dryer timer is an electronic dryness sensing printed circuit board. Electromechanical dryer timers with an electronic dryness sensing printed circuit board are widely used to control automatic dryer functions.
In prior art timers, the dryness sensing printed circuit board is mounted as an isolated component usually in the dryer console. The required electrical connections between the timer male terminals and the printed circuit board male terminals are made by wires with a standard female electrical connector for the timer and a female edge connector for the printed circuit board. Mounting a printed circuit board in this manner creates increased production costs, decreased reliability, and increased service costs compared with mounting the printed circuit board inside the timer.
Production costs are increased because an additional production step is required to mount the separate printed circuit board to the appliance console in addition to mounting the timer. Costs are further increased because mounting the printed circuit board to the appliance console is usually done with screws and the procedure is difficult to automate. During the mounting process, some printed circuit boards sustain obvious damage and require replacement slowing the production line. Additionally some printed circuit boards, wiring, or connectors sustain nonobvious damage that is difficult to detect until the appliance is test operated or, in the worst case, until the appliance purchaser discovers the problem.
Reliability is decreased when the printed circuit board is mounted as a separate component because the printed circuit board and electrical connections between the printed circuit board and timer are not protected. Field data has shown that the majority of moisture sensing circuitry failures are caused by faults in the electrical connections between the printed circuit board and timer. The unprotected printed circuit board and electrical connections are exposed to vibration, moisture, and dust. These conditions are hazardous to electronic circuitry and can cause broken printed circuit boards and loose, corroded, or dirty electrical connections. A complicating factor is that the above hazards often produce intermittent circuitry failures which are difficult to troubleshoot.
Service costs are increased because of the difficulty in troubleshooting intermittent failures and the increased labor to replace separate components. Since the moisture sensing circuitry enables and disables operation of the timer, a failure in the printed circuit board or electrical connections to the timer is often mistaken for an inoperative timer. A repairperson may replace the timer thinking the problem is solved since the fault is intermittent and appears repaired. Later if the intermitted problem reappears the repairperson will have to be recalled to replace the printed circuit board, and electrical connections.
Finally, when the separately mounted printed circuit board or electrical connections to the timer fail, the failure can cause the dryer to run continuously until the dryer is manually turned off. If the dryer runs long enough, clothing in the dryer and the appliance itself may be damaged.